Valspar Trade Knot Block Review

Updated Jun 14, 2024 | Posted Nov 1, 2022 | Product Reviews, Paints | 7 comments

Valspar Trade Knot Block is a fully water-based acrylic primer/undercoat which has been developed with stain blocking capabilities, including knot bleed. Touch dry in 30 minutes, but the recoat time is roughly 2 – 4 hours (depending on conditions). Knot Block is only available in white and costs roughly £30 for 2.5L at B&Q.


My Valspar Trade Knot Block Review


Valspar Trade Knot Block is very quick and easy to use. It flies on, and brush marks just melt away. You’ll find opacity lacking somewhat, but you should always apply two coats of this paint for it to work to the best of its abilities anyway.

I’m a bit of a decorating geek, and love developments in paint technology! At the time of writing this review, Valspar Trade have just launched a redeveloped range of paint, and they’ve really gone to town. The first on the list is Valspar Trade Knot Block, which is advertised as an acrylic undercoat. This is a massive understatement on Valspar Trade’s part, and I’ll tell you why;

Yes, you can use Knot Block as an acrylic primer/undercoat and it will perform better than most other products of its type. Not only does it prime timber, but as stated in the opening paragraph, it also stops sap from knots from bleeding through.

It doesn’t stop there though. Valspar Trade Knot Block has very good adhesion qualities, meaning you can use it as a primer over old oil-based coatings before using a water-based topcoats. I have tested it a few times, and it has always been solid.

Moreover, because Valspar Trade Knot Block is more than capable of holding back stains such as tannins, it is the perfect product for priming previously stained or varnished timber. It works too! We’re talking about a fully water-based product that flies on, sticks like sh1t to stained woodwork, is fast drying, blocks all stains, blocks knots, and leaves the perfect base for your topcoats.

The last thing you can use Knot Block for is blocking stains on plastered walls and ceiling (even though it isn’t advertised as such). Be it mould growth, permanent pen, or even water damage. You do need to stick to the two-coat-rule, but it works well. Again, it is quick and easy to apply, dries nice and fast, and is more than capable of holding back just about any stain.


Review Summary

Valspar Trade Knot Block Review - Decorator's forum UK

A water-based primer capable of carrying out many tasks.

Product Brand: Valspar Trade

Editor's Rating:


  • Blocks knot bleed.
  • Blocks stains.
  • Adheres well to different surfaces.
  • Very quick drying.
  • Creates the perfect base for other paint products.
  • Readily available.


  • Opacity isn’t great.
  • Two coats needed.

A Video Review

Valspar Trade Knot Block

A quick demo showing the capabilities of Valspar Trade Knot Block.

Best Tools to Apply Valspar Trade Knot Block


I just thought I’d touch on this quickly. Knot Block flows well, so it’s easy to apply. That said, you may need to use it to bare timber, which will make it drag. Plus, opacity isn’t Knot Block’s strong point. Therefore, I’d suggest using a brush and roller that holds and deposits plenty of paint.

My choice of paintbrush for a product like this is easy. The Purdy Monarch Elite is fantastic for Valspar Trade Knot Block and will make life a lot easier for you. Available online by clicking here.

If you have larger flat areas to paint, then a mini roller is advantageous. Again, you need it to hold loads of paint. The Purdy Jumbo Mini Roller is perfect. Available online by clicking here.


Final Thoughts


This is a brand-new product, but it’s going to be very popular amongst decorators. I think Valspar Trade tried to develop some sort of upgraded primer/undercoat, and inadvertently came up with something which has multiple uses. Valspar Trade Knot Block is like nothing I’ve ever used. To perform as well as it does, and still be so quick and easy to use is a masterpiece in my honest opinion. I can’t wait to start seeing the feedback from other decorators.



Anyone else (apart from Mike Cupit !) tried Valspar Trade Knot Block yet? I’ve used it recently on a couple of jobs as a grip primer on old oil-based gloss, before applying water-based top coats. It’s worked really well. Opacity isn’t the best, and they do recommend two coats (although I wasn’t sure if that was to get the best out of its stain-blocking capabilities or for general use as a primer), but it sticks like glue and leaves a nice smooth surface for your top coats. Looking forward to trying the Knot Block out on some stains and/or knots soon to see how it performs – but so far, pretty impressed I must say!

Valspar Trade knot block review

Robin Gofton

Updated Jun 14, 2024 | Posted Nov 1, 2022 | 7 comments

About the Author

About the Author

Mike Cupit has been in the decorating industry since 2002 and has mostly worked as a Trade Decorator in the domestic sector (peoples’ homes). Self-proclaimed “product geek”, Mike has a passion for paint and decorating tools. Mike now spends most of his time testing paint products and tools, comparing them to similar products on the market, and blogging about the industry in general.
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  1. richard

    I used white water based knot blocker years ago own house think was Ronseal it worked for a month or so then slowly burned through.

    l can remember thinking l glad tried on own house first.

    Maybe this is better fair enough, but that always sticks with me re water based knot blocker burn through in time.

    l use Fossa shallac primer from decorating direct £26 inc VAT a 2.5l pretty good gear , its not much dearer than a 1l of BIN at the merchants!

    • Phil

      Richard, you’re spot on my friend. It was Ronseal and I fell into the same trap. Unfortunately, it was for a client and I had to go back and re-do their woodwork at considerable time and cost to myself. Like yourself, a can of Fossa on the van is a must and at least you know it won’t come back and bite you. Will be interesting to see how the valspar (dreadful brand btw) performs long term.

      • Richard

        Too late now obviously but you could have billed Ronseal fingers crossed they cough up but at the very least it would be an unpaid invoice and you get tax relief on that .

  2. Michael Keyes

    Sounds too good to be true. I’ll have to give it a go.

    • Richard

      Be cautious try on own property or some knotty pine first. I be very careful here. Fossa shellac primer Decorating direct £25 approx Inc vat 2.5l
      Why risk it

  3. Sara

    Do you think you can use this product as a primer on mdf stairs too? Many thanks for any tips!

  4. Melody Loring

    I really can’t understand why anyone would want to avoid using actual “knotting” as it only takes a few minutes to run round the whole house on new woodwork and it can be painted over with primer/ undercoat in just an hour.

    Surely you can find something else to do for an hour before you need to recoat your work like prepare your walls?


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